Two inputs to a differential operational amplifier (op amp) generally cannot have exact matching characteristics. There is a slight difference between the two inputs known as input offset voltage (Vos). These offsets are amplified like any other input signal and introduce an error. The offset voltage is caused by the mismatch of transistors in the differential operational amplifier and/or other components such as resistors, and such errors may be introduced during fabrication of the device.
FIG. 1 illustrates a conventional differential op amp 100 with an input 102 and an input 104 as the two inputs. In FIG. 1, a transistor T1 is coupled to the input 102, and a transistor T2 is coupled to the input 104. The transistor T1 is also coupled to a resistor Ra, and the transistor T2 is coupled to a resistor Rb, where the resistor Ra and the resistor Rb are typically matched, and both the resistors Ra and Rb are equal to each other. The input offset voltage is a measure from the two inputs to reflect the magnitude of mismatch of all the component pairs (e.g., T1 and T2 pair, R1 and R2 pair and other component pairs not shown in FIG. 1). The input offset voltage may also change over temperature since the input offset voltage generally depends on temperature, where the measure of temperature dependence is represented as offset voltage temperature coefficient (TC Vos).